there is the united states of america. there is not a black america and a white america and latino america and asian america. there is the united states of america. >> gretchen: that was then. senator barak obama four years before he became president of the united states. the truth is, eight years after he broke on to the scene, americans seemed more polarized and divided than ever. and the question is why? let's ask larry sabato, professor of political science at the university of virginia. good morning, professor. >> good morning, gretchen. hope you're doing well. >> gretchen: we're having a good day. can i ask you that question, why do you believe such a stark change from just eight years ago when we heard the president talk about cohesion? >> gretchen, we do have a liberal america. it's the democratic party. we do have a conservative america. it's the republican party. and that's the answer to your question. we have polarized because our parties have changed dramatically over the years. there are a lot of reasons for i